A Hastings teenager who doused an acquaintance with petrol and set him alight at a party was this morning sentenced to three years in prison.

Matt-Dillion Shannon was sentenced in the High Court in Napier after a jury in found him guilty of intending to cause grievous bodily harm after a trial in September. He had earlier pleaded guilty to a charge of causing grievous bodily harm with careless disregard.

The jury took four hours to reach a verdict after a two-and-a-half day trial.

Shannon, now 18, was celebrating his 17th birthday at a party in his house on August 12 last year.

Shortly after midnight he poured petrol over a 16-year-old and set him alight with a cigarette lighter as three others held the victim down.

The victim suffered severe burns to his back, neck and one side of his face. He stripped off his burning T-shirt and rode his bicycle home before being taken to hospital and the intensive care unit.

Shannon claimed to have been copying a stunt he had seen on a Jackass movie.

While the Crown and defence had agreed Shannon's actions caused very serious harm to his victim, the defence argued he had not intended to cause such harm.

Shannon's lawyer Bill Calver had told the jury that Shannon was a drunk, testosterone-driven young man who behaved like someone "a few sandwiches short of a picnic", but there was no way he meant his victim to suffer the serious injuries he did.

The Crown and the victim said Shannon, who worked in a service station at the time, poured the petrol from a 10-litre container. Shannon said he poured it from a shot glass and used no more than 10 millilitres.

The victim, now 17, said he was held down for about 20 seconds. Shannon says it was no longer than five seconds.

Shannon told the jury the victim should have "stopped, dropped and rolled", and he would have been all right.

"I thought he'd wake up, get a fright and roll about until the flame was extinguished and he'd be fine. He just jumped up and ran around.

"If he'd stopped, dropped and rolled, it would have just been a joke instead of a serious incident."